Femtosecond Multicolor Pump−Probe Study of Ultrafast Electron Transfer of [(NH₃)₅RuIIINCRuII(CN)₅]⁻ in Aqueous Solution

Femtosecond multicolor pump−probe spectroscopy on the prototypical intramolecular electron-transfer compound ([(NH 3 ) 5 RuNCRu(CN) 5 ] -; RuRu) in aqueous solution is reported for the first time with sufficient time resolution and spectral coverage to monitor the complete spectral dynamics. From the dynamic absorption spectrum, constructed from the pump−probe data obtained over a wide range of probe wavelengths (570−1300 nm), accurate measurement of the electron transfer (ET) time (1/ k ET ) have been obtained by a global analysis of the data. The data have lead to new insights on the role of solvent and solute nuclear motions in the ET process. Additionally, pump−probe experiments with variable wavelength pump pulses have revealed the presence of a pump wavelength-dependent dynamic feature at early time, which has been assigned to stimulated emission from nonequilibrium excited states.